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I want to make a baseclass with a constructor and destructor and have
these call methods in the derived classes which vary. I though the
'template' pattern looked appropriate and tried the following, which
doesn't compile and I'm not sure why. The error message is self-
explanatory:

abstract virtual 'virtual void IClass::init()' called from constructor

but clearly I have then misunderstood the template pattern
implementation; what would be correct? why doesnt the baseclass
constructor call to init() delegate to the derived class?


#include <iostream>

class IClass{
public:
IClass(){
init();
}
protected:
virtual void init()=0;
};

class Class1ublic IClass{
public:
Class1(){
//nop
}

virtual void
init(){
std::cout<<"template method class 1"<<std::endl;
}
};

int main (int argc, char * const argv[]) {
// insert code here...
std::cout << "Hello, World!\n";
IClass * ic=new Class1();
return 0;
}

On 11 Jan., 10:47, s <shaun....@cern.ch> wrote:
> I want to make a baseclass with a constructor and destructor and have
> these call methods in the derived classes which vary.

Why?

> I though the
> 'template' pattern looked appropriate and tried the following, which
> doesn't compile and I'm not sure why. The error message is self-
> explanatory:
>
> abstract virtual 'virtual void IClass::init()' called from constructor
>
> but clearly I have then misunderstood the template pattern
> implementation; what would be correct? why doesnt the baseclass
> constructor call to init() delegate to the derived class?

See C++ FAQ 23.5

Cheers!
SG

On Jan 11, 10:55*am, SG <s.gesem...@gmail.com> wrote:
> On 11 Jan., 10:47, s <shaun....@cern.ch> wrote:
>
> > I want to make a baseclass with a constructor and destructor and have
> > these call methods in the derived classes which vary.
>
> Why?
>
> > I though the
> > 'template' pattern looked appropriate and tried the following, which
> > doesn't compile and I'm not sure why. The error message is self-
> > explanatory:
>
> > abstract virtual 'virtual void IClass::init()' called from constructor
>
> > but clearly I have then misunderstood the template pattern
> > implementation; what would be correct? why doesnt the baseclass
> > constructor call to init() delegate to the derived class?
>
> See C++ FAQ 23.5
>
> Cheers!
> SG

That's a pretty complete explanation, thanks a lot!

s <> wrote:
> why doesnt the baseclass
> constructor call to init() delegate to the derived class?

You can't call a derived class function from the constructor of the
base class because at that point the derived part has yet not been
constructed (effectively it "doesn't exist" at that point).